Application of the recently developed automated techniques has allowed quantitation of serum and red cell-bound antibodies as well as the determination of the immunological specificity and thermodynamic properties of various antigen-antibody reactions. Collectively, these laboratory parameters constitute an immunological profile, the availability of which should markedly improve the accuracy of the diagnosis of red cell incompatibility and autoimmune hemolytic diseases (AIHD). It is suggested that this profile also can be useful in determining the etiology, prognosis and selection of the appropriate therapy for individual patients with AIHD. To achieve these goals, the following research plan is proposed: 1. The serologic profile will be developed for antigen-antibody reactions of the known blood group systems, and biological implications of each parameter measured will be evaluated. 2. Similar data will be obtained for antigen-antibody reactions which occur in association with various forms of AIHD, and an attempt will be made to determine the relationship to red cell survival and other clinical manifestations. 3. Antigens involved in various forms of AIHD will be isolated and solubilized, and their chemical nature will be characterized. 4. By evaluating requirements for the optimal reactivity of various red cell antigen-antibody reactions, improved methodology will be developed for routine antibody detection and quantitation.